The ideal flow will save energy

Environmental concerns are one of the most important issues facing the shipping industry today. Developing energy saving devices (ESD) is one way of addressing this. One successful example is the so called pre-swirl stator, a device mounted close to the propeller.

Various ESDs can be applied; however some requirements have to be fulfilled in order to make a device practically applicable. Thus, it should be:

  • simple
  • relatively inexpensive to install
  • easy to maintain
  • and the design should have a solid scientific background.

One successful example is the so called pre-swirl stator, a device mounted close to the propeller. A power gain of approximate 5–6 per cent can be achieved.

Daewoo Shipbuilding and Marine Engineering Co. Ltd (DSME) has developed the pre-swirl stator (PSS) in cooperation with SSPA. The team envisions that the demand for energy saving devices (ESD) will grow even stronger, as new requirements are set up by the International Maritime Organization (IMO) concerning energy efficient design.

The PSS is a device mounted on the boss end of the hull in front of the propeller and is designed to generate pre-swirl flow in order to improve the propulsive efficiency and thus result in power reduction.

The stator configuration that has been selected from the optimisation has four blades with a diameter equal to the propeller diameter. This has become the standard configuration for a wide range of hull types including VLCCs, tankers, bulkers, Ro-Ro ships and containerships.

The design of ESDs in general requires knowledge of flow mechanisms around ESD and highly advanced Computational Fluid Dynamics (CFD) computations, coupled to accurate physical model testing. In the PSS case a wide range of design parameter variation studies was first performed with SHIPFLOW computation. The most promising configurations were then selected for the final confirmation by model tests.

SHIPFLOW computations has proved to be a sufficiently complete and accurate approach for predicting the thrust, torque and rotation rate for the propeller in order to achieve the correct ranking between different design alternatives.

The model tests confirmed the relative ranking for all PSS configurations tested. Thus, CFD simulation coupled to model testing can be a cost effective approach to develop an ideal configuration of ESDs in the future.